Additive manufacturing of metallic components – Process, structure and properties

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1037&context=mepubs

Additive manufacturing of Ti6Al4V alloy: A review

3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting

A review of selective laser melting of aluminum alloys: Processing, microstructure, property and developing trends

Today, a large number of different steels are being processed by Additive Manufacturing (AM) methods. The different matrix microstructure components and phases (austenite, ferrite, martensite) and the various precipitation phases (intermetallic precipitates, carbides) lend a huge variability in microstructure and properties to this class of alloys. This is true for AM-produced steels just as it is for conventionally-produced steels. However, steels are subjected during AM processing to time-temperature profiles which are very different from the ones encountered in conventional process routes, and hence the resulting microstructures differ strongly as well. This includes a very fine and highly morphologically and crystallographically textured microstructure as a result of high solidification rates as well as non-equilibrium phases in the as-processed state. Such a microstructure, in turn, necessitates additional or adapted post-AM heat treatments and alloy design adjustments. In this review, we give an overview over the different kinds of steels in use in fusion-based AM processes and present their microstructures, their mechanical and corrosion properties, their heat treatments and their intended applications. This includes austenitic, duplex, martensitic and precipitation-hardening stainless steels, TRIP/TWIP steels, maraging and carbon-bearing tool steels and ODS steels. We identify areas with missing information in the literature and assess which properties of AM steels exceed those of conventionally-produced ones, or, conversely, which properties fall behind. We close our review with a short summary of iron-base alloys with functional properties and their application perspectives in Additive Manufacturing.

Steels in additive manufacturing: A review of their microstructure and properties

Formation and control of martensite in Ti-6Al-4V alloy produced by selective laser melting

Selective laser melting (SLM) and laser cladding deposition (LCD) are two typical kinds of laser additive manufacturing techniques that have been developed for many years independently. Although they are based on the same principle of laser cladding, there are little comparison on the fundamental studies for metallurgical behavior (including melting and solidification behaviors) and the mechanical properties of these two techniques up to now. In this paper, the single-track formation and the deposition of block sample from 316L stainless steel powders have been carried out by both SLM and LCD techniques. A comparison on pool shape, cooling rate, columnar grain size and mechanical properties under different processing conditions by LCD and SLM respectively has been studied. It is found that, due to the increase of energy input and the decrease of depth-to-width ratio of melting pool (MP) from SLM to LCD, the primary cellular arm spacing (PCAS) of the sample increases from less than 1.0 µm to more than 15.0 µm, and thus the cooling rate of MP decreases from about 106 K/s in SLM to about 102 K/s in LCD. Furthermore, due to the decrease of cooling rate from SLM to LCD, the columnar grains of the as forming alloy are getting coarser. Especially, the relationship between gain size (λ) and the reciprocal of square root of cooling rate ( T ) in LCD significantly meets the classical linear function of λ = a + b / T (a and b are constants), while a new relationship of a cubic function is found in SLM, showing the different solidification characteristics between LCD and SLM. Lastly, the samples of 316L stainless steel by SLM have much stronger tensile strength but lower elongation than those by LCD, and the main reason is due to that the solidification behavior of the MPs by SLM can form much finer columnar grains than those by LCD.

A comparison on metallurgical behaviors of 316L stainless steel by selective laser melting and laser cladding deposition

Role of molten pool mode on formability, microstructure and mechanical properties of selective laser melted Ti-6Al-4V alloy

Inconel 718 (IN718) samples have been produced by selective laser melting (SLM). The effects of solution temperature, time and cooling rate as well as aging hardening on the microstructure and mechanical properties of SLMed IN718 have been studied. It is found that the as-fabricated IN718 is characterized with fine cellular dendrites with Laves phase precipitating in the subgrain boundaries, which is profoundly different from cast and wrought materials and needs different heat treatment schedules. The relationship between the minimum solution time and solution temperature is established and it provides a basis for the selection of solution treatment parameters. In addition, decreasing the cooling rate of solution treatment will contribute to the precipitation of strengthening phases. The precipitation temperatures of γ′ and γ″ are about the same for SLMed and wrought IN718, but the former has a faster aging response. The tensile properties of SLMed IN718 can be tuned in a large range by properly varying the microstructure. The highest elongation of 39.1% can be obtained after solution treatment (water quenching) without aging treatment and the highest yield and tensile strength (1374/1545 MPa) can be obtained after the direct aging treatment. The match of strength and ductility is able to be tailored by controlling the amount of strengthening phases, which can be realized by adjusting the cooling rate of solution treatment and aging time.

Heat treatment of Inconel 718 produced by selective laser melting: Microstructure and mechanical properties

The microstructures, potentiodynamic curves, and electrochemical impedance spectroscopy are characterized for Ti-6Al-4V samples produced by selective laser melting (SLM), SLM followed by heat treatment (HT), wire and arc additive manufacturing (WAAM), and traditional rolling to investigate their corrosion behaviors. Results show that the processing technology acts a significant role in controlling the microstructures, which in turn directly determine their corrosion resistance. The order of corrosion resistance of these samples is SLM < WAAM < rolling < SLM+HT. Among these microstructural factors for influencing corrosion resistance, type of constituent phase is the main one, followed by grain size, and the last is morphology. Finally, the application potentials of additive manufactured Ti-6Al-4V alloy are verified in the aspect of corrosion resistance.

Zemin Wang

Papers

Formation and control of martensite in Ti-6Al-4V alloy produced by selective laser melting

A comparison on metallurgical behaviors of 316L stainless steel by selective laser melting and laser cladding deposition

Role of molten pool mode on formability, microstructure and mechanical properties of selective laser melted Ti-6Al-4V alloy

Heat treatment of Inconel 718 produced by selective laser melting: Microstructure and mechanical properties

Corrosion Behavior of Additive Manufactured Ti-6Al-4V Alloy in NaCl Solution